Background: Tuberculosis is a life threatening disease caused by mycobacterium tuberculosis. In developing countries the incidence of tuberculosis has been increasing steadily since the 1990s, particularly in African countries. Several European countries have lately reported a slight increase in tuberculosis, but these are mostly related to immigrants from high-incidence countries. Objective: To assess the treatment outcomes of tuberculosis and its associated factors among tuberculosis patients on anti-tuberculosis therapy in Nekemte Referral Hospital, West Ethiopia. Methods: A four years retrospective cross-sectional study was used and all patients’ information that fulfilled the inclusion criteria was retrieved from records of patients with basic information for all registered patients. We analyzed the records of 315 tuberculosis patients who had known outcome in Nekemte Referral Hospital from September 2012-August 2016. Results: From the total of 315 patients who had known treatment out come in Nekemte Referral Hospital, tuberculosis type was categorized as smear positive pulmonary TB in 68(21.5%), smear negative pulmonary TB in 107(34.0%), and extra pulmonary in 140(44.4%) cases. Records of the 315 TB patients showed that 54(17.01%) were cured, 206(65.4%) completed treatment, 24(3.5%) had treatment failure, 11(3.5%) defaulted, 20(6.3%) were died. The overall treatment success rate of the TB patients was 82.5%. Age ≥ 45 years (AOR=7.1, 95% CI=1.5-34.3, p=0.014), smear negative PTB (AOR=3.4, 95%, CI=1.5-9.5, P=0.023) and retreatment cases (AOR=12.0, 95%, CI=4.2-34.4, P<0.001) were significantly associated with unsuccessful treatment outcome. Conclusion: Successful treatment outcome of TB patients was below standard. To improve treatment outcome among TB patients health education on the importance of TB treatment and the consequences of poorly treated TB have to be provided to patients during their follow up.